Unwanted carriage return character on COM port

[NewtownGuy]

Hello,

I'm creating command strings that I sent out ttyS0 to control a robot. The strings are less than 10 bytes long and have binary data.

The problem is that every time I output a byte that happens to be 0x0A -- line feed -- a leading carriage return -- 0x0D -- gets added somewhere. This wrecks the command string.

I'm running Fedora Core 3. I'm guessing that the problem is with outputting the binary string through the COM1 / ttyS0 port because the binary log files we create are correct. If the COM port is the problem, how should we fix it ?

Here's how we configure the COM port at bootup in rc.local:

#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

setserial /dev/ttyS0 divisor 12
setserial /dev/ttyS0 spd_cust
setserial /dev/ttyS0 baud_base 115200
setserial /dev/ttyS0 close_delay 50
setserial /dev/ttyS0 closing_wait 100

chown root:apache /dev/ttyS0
chmod 666 /dev/ttyS0

We used divisor and spd_cust to get 9600 baud because the port kept running at 115,200 when we used baud_base 9600 with the default divisor. The chown line is shown because we provide the command strings through IE through apache, and we print the command strings to /dev/ttyS0.

Thank you.

-- NewtownGuy

 

[thedaver]

What is the script doing? Code?

D.E.R. Management - IT Project Management Consulting

http://www.dermanagement.com/

 

[NewtownGuy]

TO: thedaver,

It's the standard rc.local script that runs at startup, to which we've added COM port initialization and two properties lines. The comment is the standard one from the Fedora Core 3 distribution.

-- NewtownGuy

 

[hoinz]

Hello NewtownGuy,

I remember having done something like that years ago on some flavour of Unix, and I suppose it should work in a similar way for Linux:
In your manual pages for stty pay attention to -inlcr. Not sure if the same goal may be achieved with setserial or other commands.

hope this helps

 

[hoinz]

... or rather -onlcr
(i for input, o for output)

 

[NewtownGuy]

TO: hoinz (MIS)

Thank you ! Using "stty --file=/dev/ttyS0 -onlcr -ocrnl" fixed the problem ! (I added protection for both LF and CR.)

-- NewtownGuy